THE CIRCULATION 253 



1st. The rate of the pulse i.e. the rate of the heart's 

 action. 



2nd. The rhythm of the pulse i.e. of the heart's action as 

 regards (1) Strength of the various beats. Normally the 

 beats differ little from one another in force since the 

 various heart beats have much the same strength. Respira- 

 tion has a slight effect which will afterwards be considered 

 (see p. 295). In pathological conditions great differences in 

 the force of succeeding pulse waves occur. (2) Time relation- 

 ship of beats. Normally the beats follow one another at 

 regular intervals somewhat shorter during inspiration 

 somewhat longer during expiration. In pathological con- 

 ditions great irregularities in this respect may occur. 



3rd. The volume of the pulse wave. Sometimes the wave 

 is high and greatly expands the artery sometimes less high 

 and expanding the artery less. The former condition is called 

 a full pulse (pulsus plenus), the latter a small pulse (pulsus 

 parvus). The fulness of the pulse depends upon two factors. 

 1st. The average tension in the arteries between the pulse beats. 

 If this is high, the walls of the artery are already somewhat 

 stretched, and therefore the pulse wave expands them further 

 only slightly. On the other hand, if the average pressure is 

 low, the arterial wall is lax, and is readily stretched to a greater 

 extent. 2nd. The force of the heart. To stretch the arterial 

 wall to a large extent requires an actively acting heart throw- 

 ing a sudden large wave of blood into the arterial system at 

 each systole. The full pulse is well seen after violent exer- 

 tion, when the heart is active and the peripheral vessels fully 

 dilated, thus allowing a free flow of blood from the arteries 

 and thus keeping the mean arterial pressure low. 



4:th. Tension of the pulse. Sometimes the pulse wave is 

 easily obliterated by pressing on the artery sometimes con- 

 siderable force is required to prevent it from passing. To 

 test this two fingers must be placed on the artery. That 

 placed nearest the heart must be pressed more and more 

 firmly on the vessel until the pulse wave is no longer felt by 

 the second finger. In this way the tension or force of the 

 pulse may be roughly determined. So important, however, 

 is this point that various instrumental methods for deter- 

 mining it have been devised. 



